These replacement atomizer heads feature pure organic Japanese cotton wicks. The 0.15 ohm coils are wrapped from pure Nickel (NI-200) wire, allowing you to monitor and limit the temperature your coils are reaching. Because these coils are only for use on temperature sensing devices like the Evolv"s DNA 40 board, the silicone rings are blue for ease of identification. Get performance and peace of mind, pick up the new temperature sensing OCC coils for your Subtank today!